cs Java: lecture #5

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1 cs Java: lecture #5 news: homework #4 due today homework #5 out today today s topics: applets, networks, html graphics, drawing, handling images graphical user interfaces (GUIs) event handling interfaces cs java-spring2003-sklar-lect05 1

2 networks (1). two or more computers connected to each other networked computers can share information and resources, e.g.: printer file server example: CUNIX system connections: point-to-point computers are directly connected to each other message speed is fast adding computers is expensive single communication line message speed can be slow adding computers is cheap cs java-spring2003-sklar-lect05 2

3 networks (2). network address uniquely identifies each computer on the network packet long messages are split into pieces each piece is a packet, sent individually along the network improves message speed local-area network (LAN) designed to span short distances wide-area network (WAN) designed to span longer distances connects multiple LANs cs java-spring2003-sklar-lect05 3

4 networks (3). the Internet developed in the 1970s as ARPANET the ultimate WAN a network of networks protocol set of rules governing communication TCP/IP (transmission control protocol / internet protocol) IP address = network address on the Internet numeric, e.g., also have text equivalents called Internet addresses, which are comprised of local computer names (i.e., name of computer on LAN) plus domain names (i.e., name of LAN on WAN) domain names are controlled by the Internet Naming Authority domain name system (DNS) translates between IP address and Internet address cs java-spring2003-sklar-lect05 4

5 networks (4). the World Wide Web (WWW) provides standard method of interfacing to the Internet from the user level uses hypertext non-linear method of organizing information refers only to textual information hypermedia refers to non-textual information, such as sound, video and graphics browser user program that provides method of viewing WWW documents early browsers included: Archie, Gopher Mosiac first graphical WWW browser released in 1993 became Netscape cs java-spring2003-sklar-lect05 5

6 networks (5). HyperText Markup Language (HTML) standard format for WWW documents Uniform Resource Locator (URL) unique document address on the WWW HypterText Transfer Protocol (http) protocol used for transfering HTML documents provides one-way transfer from server to client other protocols include: ftp, telnet these provide two-way transfer between server and client Java grew out of the above allows two-way transfer text, graphics, sound cs java-spring2003-sklar-lect05 6

7 networks (6). client-server architecture comes from operating system design methodology by which tasks are divided onto different processors according to functionality programs can be divided into: computation portion drawing or output portion each portion can be executed on a different CPU X windows windowing system used under UNIX with X windows, the drawing is done on the client, although the execution may be happening on a different physical machine, the server cs java-spring2003-sklar-lect05 7

8 applets (1). Java programs can run as applications or applets application: executed using the java command server and client can be the same machine or different machines client invokes JVM which interprets classes and runs them applet: must be executed using a browser, like Netscape, or the appletviewer command server sends applet to the client, in the form of class files; applet invokes JVM which interprets classes and runs them on the client there are two parts: an HTML file used to invoke the applet Java class file(s) that contain the applet code cs java-spring2003-sklar-lect05 8

9 applets (2). file name = hi.html <html> <title> sample applet page </title> the applet will be shown below... <applet code="hi.class" width=400 height=400> </applet> </html> cs java-spring2003-sklar-lect05 9

10 applets (3). file name = hi.java import java.awt.*; import java.applet.applet; public class hi extends Applet { public void paint( Graphics g ) { g.drawstring( "hi",10,10 ); } // end of paint() } // end of class hi cs java-spring2003-sklar-lect05 10

11 applets (4). java.awt package Abstract Windowing Toolkit (AWT) classes that support graphical user interfaces (GUI) includes java.awt.component method: public void paint() java.applet.applet class public void init() public void start() public void stop() cs java-spring2003-sklar-lect05 11

12 frames (1). used when you want to write an application that has graphics relationship between Frame and Applet: java.lang.object +--java.awt.component +--java.awt.container +--java.awt.panel +--java.applet.applet java.lang.object +--java.awt.component +--java.awt.container +--java.awt.window +--java.awt.frame cs java-spring2003-sklar-lect05 12

13 frames (2). import java.awt.*; public class hiho extends Frame { mycanvas c; public hiho( String title ) { super( title ); } // end of hiho constructor public static void main( String[] args ) { hiho h = new hiho( "myframe!" ); h.c = new mycanvas(); h.add( h.c ); h.setsize( 100,100 ); h.setbackground( Color.red ); h.show(); } // end of main() } // end of class hiho cs java-spring2003-sklar-lect05 13

14 frames (3). import java.awt.*; public class mycanvas extends Canvas { public Dimension getminimumsize() { return( new Dimension( 90,90 )); } // end of getminimumsize() public void paint( Graphics g ) { setbackground( Color.blue ); g.drawstring( "hiho",10,10 ); } // end of paint() } // end of class mycanvas cs java-spring2003-sklar-lect05 14

15 graphics (1). java.awt.graphics class X-windows coordinate system drawing primitives: lines Strings rectangles ovals arcs color cs java-spring2003-sklar-lect05 15

16 graphics (2). simple methods from the java.awt.graphics class void drawline( int x1, int y1, int x2, int y2 ); draws a line connecting (x1,y1) and (x2,y2 ); void drawstring( String str, int x, int y ); draws the text in str, with its lower left corner at (x,y) cs java-spring2003-sklar-lect05 16

17 graphics (3). import java.awt.*; import java.applet.applet; public class hi2 extends Applet { public void paint ( Graphics g ) { g.drawstring( "hello world!",10,10 ); g.drawline( 0,400, 400,0 ); } // end of paint() } // end of class hi2() cs java-spring2003-sklar-lect05 17

18 graphics (4). bounding rectangles coordinates of origin (upper left corner) extent (width and height) arcs measured in degrees starting from 0 (along positive X-axis) extent (total angle of arc) cs java-spring2003-sklar-lect05 18

19 graphics (5). methods from the java.awt.graphics class for drawing outlines of shapes void drawrect( int x, int y, int width, int height ); draws a rectangle with its upper left corner at (x,y), extending the specified width and height void drawoval( int x, int y, int width, int height ); draws an oval circumscribed in the bounding rectangle with its upper left corner at (x,y), extending the specified width and height void drawarc( int x, int y, int width, int height, int startangle, int arcangle ); draws an arc whose oval is circumscribed in the bounding rectangle with its upper left corner at (x,y), extending the specified width and height, where the arc starts at the startangle, measured in degrees (where 0 ) is horizontal along the positive x-axis), extending for arcangle degrees cs java-spring2003-sklar-lect05 19

20 graphics (6). import java.awt.*; import java.applet.applet; public class hi3 extends Applet { public void paint ( Graphics g ) { g.drawrect( 10,300,25,25 ); g.drawoval( 10,250,25,25 ); g.drawarc( 10,200,25,25,45,90 ); } // end of paint() } // end of class hi3() cs java-spring2003-sklar-lect05 20

21 graphics (7). methods from the java.awt.graphics class for drawing filled shapes void fillrect( int x, int y, int width, int height ); draws a filled rectangle with its upper left corner at (x,y), extending the specified width and height void filloval( int x, int y, int width, int height ); draws a filled oval circumscribed in the bounding rectangle with its upper left corner at (x,y), extending the specified width and height void fillarc( int x, int y, int width, int height, int startangle, int arcangle ); draws a filled arc whose oval is circumscribed in the bounding rectangle with its upper left corner at (x,y), extending the specified width and height, where the arc starts at the startangle, measured in degrees (where 0 ) is horizontal along the positive x-axis), extending for arcangle degrees cs java-spring2003-sklar-lect05 21

22 graphics (8). methods from the java.awt.graphics class for drawing polygons void drawpolygon(int[] xpoints, int[] ypoints, int npoints); draws a closed polygon defined by arrays of x and y coordinates void drawpolygon( Polygon p ); draws the outline of a polygon defined by the specified Polygon object void drawpolyline( int[] xpoints, int[] ypoints, int npoints ); draws a sequence of connected lines defined by arrays of x and y coordinates the first two have counterparts for drawing filled polygons: void fillpolygon(int[] xpoints, int[] ypoints, int npoints); void fillpolygon( Polygon p ); cs java-spring2003-sklar-lect05 22

23 graphics (9). java.awt.color class color is defined using the RGB methodology Red, Green, Blue each is an integer between 0 and 255, where 0 means no color and 255 means maximum color so white is: red=255 green=255 blue=255 or the ordered triple (255,255,255) and black is: red=0 green=0 blue=0 and red is: red=255 green=0 blue=0 and green is: red=0 green=255 blue=0 and blue is: red=0 green=0 blue=255 make up your own colors... cs java-spring2003-sklar-lect05 23

24 graphics (10). even more methods from the java.awt.graphics class void setcolor( Color color ); sets the foreground (pen) color to the specified color void fillrect( int x, int y, int width, int height ); draws a filled rectangle with its upper left corner at (x,y), extending the specified width and height void filloval( int x, int y, int width, int height ); draws a filled oval circumscribed in the bounding rectangle with its upper left corner at (x,y), extending the specified width and height void fillarc( int x, int y, int width, int height, int startangle, int arcangle ); draws a filled arc whose oval is circumscribed in the bounding rectangle with its upper left corner at (x,y), extending the specified width and height, where the arc starts at the startangle, measured in degrees (where 0 ) is horizontal along the positive x-axis), extending for arcangle degrees cs java-spring2003-sklar-lect05 24

25 graphics examples. snowman.java bullseye.java snowman2.java, man.java (with helper class) snowman3.java (animated) snowman4.java (another way of doing animation) cs java-spring2003-sklar-lect05 25

26 GUIs (1). GUI = Graphical User Interface java.awt classes: Component Container LayoutManager Event java.awt.event classes: ActionListener ItemListener KeyListener MouseListener MouseMotionListener cs java-spring2003-sklar-lect05 26

27 GUIs (2). components a component is a building block of any GUI here are some examples: Label TextField, TextArea Button Checkbox, CheckboxGroup Choice List cs java-spring2003-sklar-lect05 27

28 GUIs (3). containers a container is a special component that can hold other components here are some examples: Applet Frame Panel cs java-spring2003-sklar-lect05 28

29 GUIs (4). layout managers a layout manager describes where the components are laid out within a given container you need to set the layout manager for each container you can nest containers (and their layour managers) BorderLayout simplest layout manager looks like this: north west center east south GridBagLayout more complex layout manager; but gives you the most control cs java-spring2003-sklar-lect05 29

30 GUIs (5). listeners are interfaces you need to implement the appropriate listener(s), depending on what events you want to handle then you need to override each method in the interface e.g., for a KeyListener, you need: keypressed() keytyped() keyreleased() the body of a method can be empty, if you don t want to do anything when a given event occurs cs java-spring2003-sklar-lect05 30

31 events (1). an event represents some action on the part of the user user-generated events are entered either through the mouse or the keyboard examples: mouse pressed mouse released mouse clicked mouse entered mouse exited mouse moved mouse dragged cs java-spring2003-sklar-lect05 31

32 listeners (1). a listener is a part of a program that captures these events for processing in the program frequently, a listener interface is created for example, java.awt.event.mouselistener: void mousepressed( MouseEvent evt ); void mousereleased( MouseEvent evt ); void mouseclicked( MouseEvent evt ); void mouseentered( MouseEvent evt ); void mouseexited( MouseEvent evt ); what is a MouseEvent? Point getpoint(); int getx(); int gety(); int getclickcount(); cs java-spring2003-sklar-lect05 32

33 listeners (2). another example, java.awt.event.keylistener: void keypressed( KeyEvent evt ); void keyreleased( KeyEvent evt ); void keytyped( KeyEvent evt ); what is a KeyEvent? char getkeycode(); cs java-spring2003-sklar-lect05 33

34 GUI examples. MouseListener examples: Dots.java Dots2.java Dots3.java KeyListener examples: Dots4.java Dots5.java gui.java, snowflake.java cs java-spring2003-sklar-lect05 34

35 interfaces (1). an interface is a group of abstract methods that are defined by all classes that implement the interface an abstract method is one that does not have an implementation, i.e., there is no body of code for the method polymorphism means having many forms lets us use different implementations of a single interface binding happens when a particular implementation is locked to an interface this can happen at compile time or at run time an example of a run-time or dynamic binding is: ((Philosopher)current).pontificate(); from the example to follow cs java-spring2003-sklar-lect05 35

36 interfaces (2). public interface Speaker { public void speak(); public void announce( String str ); } // end of Speaker interface cs java-spring2003-sklar-lect05 36

37 interfaces (3). public class Philosopher implements Speaker { private String philosophy; public Philosopher ( String thoughts ) { philosophy = thoughts; } // end of Philosopher constructor public void speak () { System.out.println( philosophy ); } // end of Philosopher method speak public void announce ( String announcement ) { System.out.println( announcement ); } // end of Philosopher method announce public void pontificate() { for ( int i=0; i<5; i++ ) System.out.println( philosophy ); } // end of Philosopher method pontificate } // end of Philosopher class cs java-spring2003-sklar-lect05 37

38 interfaces (4). public class Dog implements Speaker { public void speak() { System.out.println( "woof" ); } // end of Dog method speak public void announce( String arf ) { System.out.println( "woof: " + arf ); } // end of Dog method announce } // end of class Dog cs java-spring2003-sklar-lect05 38

39 interfaces (5). public class Talking { public static void main( String[] args ) { Speaker current; current = new Dog(); current.speak(); current = new Philosopher( "I think, therefore I am." ); current.speak(); ((Philosopher)current).pontificate(); } // end of main() } // end of Talking class cs java-spring2003-sklar-lect05 39

40 exercise. look at the examples in the class web page: cs3101/examples/gallery.html copy the code for one of the snowman examples copy the code for the gui example replace the snowflake in the gui with the snowman change the components of the gui to do something interesting with the snowman cs java-spring2003-sklar-lect05 40

41 advanced graphics (1): fonts. fonts in Java are defined using the java.awt.font class you can see which fonts (by name) are available in your system by using the java.awt.graphicsenvironment.getallfonts() method you can get information about the point size of the font, whether it is italic, bold or plain you will most likely want to get the size of a string that might be drawn with the current font. first you need to create a FontMetrics object, then you can call the FontMetrics.stringWidth( String str ) method to find the width cs java-spring2003-sklar-lect05 41

42 advanced graphics (2): fonts, continued. useful font properties available in FontMetrics: ascent the distance from the font s baseline to the top of an alphanumeric character use int FontMetrics.getMaxAscent() descent the distance from the font s baseline to the bottom of an alphanumeric character with descenders use int FontMetrics.getMaxDescent() height the distance between the baseline of adjacent lines of text; the sum of the leading + ascent + descent. leading aka interline spacing; the logical amount of space to be reserved between the descent of one line of text and the ascent of the next line advance the distance from the leftmost point to the rightmost point on the string s baseline use int FontMetrics.charWidth( char ch ) to get the advance of the char argument cs java-spring2003-sklar-lect05 42

43 advanced graphics (3): images. you can load images from a URL and draw them load them using java.applet.getimage( URL url ) for an applet or java.awt.toolkit.getimage( URL url ) for an application draw them using Graphics.drawImage() this method there are a number of versions of note that an Image is a Java object unto itself, defined in the java.awt package also note that URL is a Java object that must be instantiated prior to using either of the getimage() methods cs java-spring2003-sklar-lect05 43

44 advanced graphics (4): animation. computer animation is kind of like an old-fashioned flip book you need to draw the object(s) being animated repeatedly, in each new location each time, you calculate the new position of the object(s) and redraw you can either redraw the entire scene or you can only redraw the object(s) that are moving but in the second case, you need to erase the object first, then move it to its new location and redraw the erasing part can be tricky if the background is not solid cs java-spring2003-sklar-lect05 44

45 advanced graphics (5): GridBagLayout. GridBagLayout you place components in the container in rows and columns you can specify the number of rows and columns you can specify the spacing between each row and/or column you can specify how a component is placed within its row/column, if it is smaller than the space allocated note that the height of an entire row is uniform, even if the components in each column are of different heights and the same for the width of a column all these are specified using a GridBagConstraints object cs java-spring2003-sklar-lect05 45

46 advanced graphics (6): GridBagLayout, continued. GridBagConstraints( int gridx, int gridy, int gridwidth, int gridheight, double weightx, double weighty, int anchor, int fill, Insets insets, int ipadx, int ipady ); gridx, gridy specify the location of the component, starting from (0,0) gridwidth, gridheight specify how many columns/rows the component occupies weightx, weighty specify how to distribute extra horizontal and vertical space anchor specifies where to place a component when it is smaller than its display area (e.g., CENTER, NORTH, NORTHEAST,...) fill specifies whether to resize a component if it is smaller than its display area (e.g., NONE, HORIZONTAL, VERTICAL, BOTH) insets specifies minimum amount of space between a component and the edges of its display area (external padding) ipadx, ipady specifies how much space to add to the minimum width and height of the component (internal padding) cs java-spring2003-sklar-lect05 46

Graphics Applets. By Mr. Dave Clausen

Graphics Applets. By Mr. Dave Clausen Graphics Applets By Mr. Dave Clausen Applets A Java application is a stand-alone program with a main method (like the ones we've seen so far) A Java applet is a program that is intended to transported